Identification of the promising mango (Mangifera indica L.) genotypes based on morphological and pomological characters

Abstract Mango (Mangifera indica L.) is one of the choicest fruit crops of the tropical and subtropical regions in the world. Morphological and pomological diversity of 18 mango (M. indica) genotypes (with 3–10 replications for each genotype, 81 trees in total) was evaluated from four areas of Sistan‐va‐Baluchestan province, Iran. There were significant differences among the genotypes investigated based on the traits recorded. Harvest date ranged from late May to early August. Fruit skin ground color was highly variable, including light green, green, light yellow, yellow, and orange. The values of fruit dimensions‐related characters were as follows: fruit length: 45.67–142.21 mm, fruit diameter: 37.51–94.13 mm, and fruit weight: 44.58–469.42 g. Peel and pulp percentages ranged from 65.24 to 92.45%. The quantity of fiber on stone was intermediate in most of the genotypes. Fruit weight showed positive standardized beta‐coefficient (β) values with stone weight (β = 0.66, p < .00) and pulp and skin content (β = 0.44, p < .00). Thus, these two key variables are the main traits accounting for fruit weight, and they should be considered together in breeding programs. Principal component analysis (PCA) showed 21 components explaining 85.44% of the total variance, and the first principal component (PC1) was positively correlated with fruit‐related traits. A dendrogram created using Euclidean distances and the Ward's method revealed two main clusters. High dissimilarity levels among the studied genotypes showed high variability in the germplasm. Based on the traits related to fruit quality, seven genotypes, including GulabKhas, Chaunsa, Ghalami, Soldan, Porteghali, KalmiBozorg, and Jangal, were superior and are recommended to use for cultivation in commercial orchards for area‐specific and in breeding programs.


| The characters evaluated
In total, 82 morphological and pomological variables were applied to investigate phenotypic variability among the genotypes (Table 1).
Morphological and pomological evaluations were carried out using 50 replications of leaves and fruits per genotypes. The dimensions of leaf, fruit, stone, and seed were measured using a digital caliper. The weight of fruit, stone, and seed was measured using an electronic balance with 0.01 g precision. The remaining characters were qualitatively measured using rating and coding (

| Statistical analysis
Analysis of variance (ANOVA) was performed to evaluate the variation among genotypes based on the traits measured using SAS software (SAS Institute, Cary, NC, USA, 1990). Simple correlations between traits were determined using Pearson correlation coefficients (Norusis, 1998). Principal component analysis (PCA) was used to investigate the relationship between genotypes and determine the main traits effective in genotype segregation using SPSS software. Hierarchical cluster analysis (HCA) was performed using Ward's method and Euclidean coefficient using PAST software (Hammer et al., 2001). The first and second principal components (PC1/PC2) were used to create a scatter plot with PAST software.
Besides, independent traits affecting the fruit weight as a dependent trait were determined through multiple regression analysis (MRA) using the "linear stepwise" method with SPSS software.

| RE SULTS AND D ISCUSS I ON
There were significant differences among the genotypes investigated based on the traits recorded. Also, the CV was more than 20.00% in 75 out of 82 characters measured, indicating high diversity among the genotypes. Depth of fruit stalk cavity showed the highest CV (127.02%), followed by fruit neck prominence (106.70%), presence of and adherence of fiber to fruit skin (70.27%). In contrast, the lowest CV belonged to pulp and skin content (6.84%) ( Table 1).
Red blush may develop in some fruits at fruit set which may persist until the fruit ripe. The red blush in mango skin is also genotype dependent due to a pigment known as anthocyanin (Bally, 2006;Khan et al., 2015;Lizada, 1991).
Fruit skin surface texture was predominantly smooth (74 genotypes). Pulp color of ripe fruits showed strong variability and included light yellow (3), yellow (18) (Bhamini et al., 2018;Chatterjee et al., 2005;Gupta & Brahmachari, 2004;Mannan et al., 2003). These variations might be due to the location enjoying different types of environmental conditions, year of production, and out crossing among different varieties (Bhamini et al., 2018;Mannan et al., 2003). The topic of fruit growth and development may be influenced by genes, proteins as well as agronomic practices, climate, and other mechanical processes that specify or affect the fruit formation and development. Plants compromised in photosynthesis, phloem transport, floral initiation and development, or male or female fertility either cannot produce fruit or are abnormal in their fruit production, that is, parthenocarpic fruit, reduced fruit size, or reduced fruit load (Tanksley, 2004). Khan et al. (2015) also reported that even if a variety of mango being grown in the same region, its quality will be affected by different environmental conditions.
Quantity of fiber on stone was low (14 genotypes), intermediate  (Khan et al., 2015;Tisserat et al., 1979). Nucellor embryony is also present in mango discovered in 19 mango cultivars (Khan et al., 2015;Sachar & Chopra, 1957). Adventive embryony (adventitious embryogenesis) established by the influence of single or more genes has been observed in mango. Eastern Indian cultivars consist of monoembryonic variations due to presence of overriding genes, while Cochin, China, Philippines, and Sunda Islands are polyembryonic due to the impact of recessive genes (Khan et al., 2015;Prasad & Prasad, 1972). The presence of polyembryony or monoembryony traits is most critical in germplasm characterization. So, mango cultivars have been classified into two major categories depending upon the type of embryo, that is, monoembryony and polyembryony (Iyer & Degani, 1997;Khan et al., 2015). Monoembryonic mango seed consists of only one embryo, usually having lobed shape and unequal in size; whereas, polyembryonic seed contains more than one embryo, among them one is zygotic and others arise from nucellus. The pictures of different organs of M. indica genotypes studied are shown in Figure 1.
After calculating the simple correlation coefficients, fruit weight was considered as a dependent variable, and then the direct and indirect effects of each independent variable on this key trait were calculated using MRA. The MRA showed that fruit weight was found to be associated with 18 characters (Table 3). Fruit weight showed positive standardized beta-coefficient (β) values with stone weight (β = 0.66, P < 0.00) and pulp and skin content (β = 0.44, P < 0.00).
Thus, these two key variables are the main traits accounting for fruit weight, and they should be considered together in breeding pro- grams. An understanding association between these traits can help breeders for selection and crosses (Khadivi-Khub & Ebrahimi, 2015).
The most important variables influencing to distinguish the variations among the genotypes were determined using the PCA.
Eigenvalues greater than 1.00 were highlighted as criteria to extract the main components, to determine the PCs that showed the greatest value of diversity. The loaded values ≥0.53 were considered significant for each factor, which showed 21 components with explaining 85.44% of the total variance (not shown). The PC1 was positively correlated with fruit length, fruit diameter, fruit weight, fruit attractiveness, fruit pulp thickness, stone length, stone width, stone thickness, stone weight, seed length, seed width, seed thickness, and seed weight, accounting for 12.45% of total variance. Thus, PC1 could be called as fruit-related traits. Five traits, including leaf blade length, leaf blade width, petiole length, petiole thickness, and thickness of pulvinus were significantly and positively correlated with PC2, accounting for 6.01% of total variance. Thus, PC2 could be called as vegetative-related traits. The PC3 was associated with quantity of fiber in pulp, adherence of fiber to fruit skin, fiber length in the pulp, and pulp juiciness, accounting for 5.35% of total variance.
The projection of the studied genotypes based on the PC1/ PC2 plot reflected the relationship among them in terms of phenotypic resemblance (Figure 2). By starting from negative toward positive values of PC1, the genotypes showed gradual increases in fruit length, fruit diameter, fruit weight, fruit attractiveness, fruit pulp thickness, stone length, stone width, stone thickness, stone weight, seed length, seed width, seed thickness, and seed weight.